An automobile wheel bolt hole, a ball socket and a platform pertain to the mating feature of a fastening bolt and a hub, and involve the safety, so paint films are not allowed. In the present hub coating production, small plug or ball protectors are generally adopted, and the sizes of the protectors corresponding to different wheels are different, so a large number of different protectors are needed; and paint drop treatment must be performed after the protectors are used for a period of time, and many hazardous wastes may be produced, resulting in noncompliance with the requirements of enterprises for green, lean and automatic development.